Www.slideshare.net is a website that lets you upload your own Powerpoint presentations to share them with others on the internet, and to download those made by other people. It's a great teaching resource, as you'll see when you browse the categories.
If you are interested in a (long) presentation about the mobile web, i.e. being able to access the Internet via a mobile device, e.g. an iPhone or a Blackberry, you might like to listen to this presentation by Jason Grigsby.
Even if you are not interested in mobile web technology, but think some of your students might be, give them the link to this blog and tell them to listen to a real live presentation about the mobile web by a native speaker who knows lots of geeky words. They might actually appreciate it.